Perhaps something should have been deleted in the highlighted text below (from spec version 0/28, section 4.6—HTML blocks, second paragraph).
There are seven kinds of HTML block, which can be defined by their start and end conditions. The block begins with a line that meets a start condition (after up to three spaces optional indentation). It ends with the first subsequent line that meets a matching end condition, or the last line of the document or other container block), if no line is encountered that meets the end condition. If the first line meets both the start condition and the end condition, the block will contain just that line.
Note: I’m not sure this is the place to note this bug. If it isn’t, I’m happy to report it through the correct channel.